Swansea may be 5-1 up heading into the second leg of their Europa League play-off against Petrolul Ploiesti in Romania, but manager Michael Laudrup claims he is concerned.

As with their third qualifying round tie against Malmo, Swansea dominated the home leg against the Romanian cup holders and sealing a place in the group stages of the tournament should be a mere formality at Stadionul Ilie Oana.

Swansea's decision to travel to Romania without captain Ashley Williams, record signing Wilfried Bony and Jonjo Shelvey, as the trio nurse slight injuries which will not keep them out of Sunday's Premier League game at West Brom, would suggest the Welsh club believe the job is done.

However, the Dane has sounded a note of caution ahead of the return meeting and has reminded his players a failure to approach the game with the right attitude could yet see them become the victims of a remarkable turnaround.

In fact, should Petrolul advance they would be only the third club in the history of this tournament to overturn a four-goal deficit from the first leg.

But, Laudrup said: "I have concerns, tomorrow we will play against a team who have nothing to lose. They had a huge result go against them last week, losing 5-1.

"So they can just go out and take chances, go forward and try to get an early goal. So we have to be ready from the first minute, that is for sure.

"For a club like us, we want to go on in European competition, into the group stage, so we know we have a job to do.

"Winning 5-1 was a huge result, but once in a while there are miracles and they can happen if you do not have the right attitude. But I am confident we will be competitive and try to win the game tomorrow, not just on aggregate but on the night."

Swansea are also without Nathan Dyer (hamstring) and Neil Taylor (thigh) due to injury, but the club have strengthened their full-back resources after re-signing Dwight Tiendalli on a three-year contract.

Tiendalli made 25 appearances last year having been signed after Taylor broke his ankle.

The Dutchman will not be involved in Romania, but could come into contention for the weekend trip to The Hawthorns.

Taylor is due to be out for four to six weeks, but Laudrup was keen to make it clear he has not signed Tiendalli due to any long-term worries over the Wales international's fitness.

"I can confirm Dwight has re-signed," he said. "But I don't want to talk about it too much now as we have a game on Thursday.

"We know him so we know exactly what he can give us. I think Neil will come back but we know Dwight and it is always good to know a player as you know what you will get."

The absence of Williams means club stalwart Leon Britton will lead the Swans, and the 30-year-old admits it will be a special moment.

"It is something I am very proud of," he said.

"I was fortunate to lead the side out twice against Arsenal last season, but it will be great to lead the side out in European competition because it is new for the club and it means a lot to me."